The present invention relates to cleaning methods and, more particularly, to a method utilizing ultrasonic means to effect cleaning and decontamination of the external or internal surfaces of nuclear fuel casks.
The shipping casks for radioactive materials in nuclear generating plants must be decontaminated to an acceptable level before leaving the plant. Currently, the external surfaces of spent fuel casks are cleaned either by high velocity water jets or by manual scrubbing. Both methods require long time periods for adequate cleaning. Typically, three or four days of continuous cleaning are required in order to bring the radiation down to acceptable levels for shipment. Moreover, large amounts of radioactivity are released to the atmosphere by water jet cleaning, and workers may receive large radiation doses when cleaning the casks manually. The internal surfaces of the casks are usually steam cleaned and, while being generally smooth and presenting less cleaning problems than the external surfaces, involve considerable time and expense in reaching acceptable levels of radioactivity.
It is apparent, therefore, that the economic disadvantage associated with extended cleaning periods, together with the radiation hazards, render present cleaning methods undesirable. The present invention has a principal object the provision of a method for cleaning nuclear fuel shipping casks which is much faster than presently used methods, as well as safe and effective.
A further object is to provide a novel cleaning method of general application utilizing ultrasonic means.
Other objects will in part be obvious and will in part appear hereinafter.